Zero emission natural gas power and liquefaction plant

Abstract

A zero-emissions power plant receives natural gas from wells at elevated pressure and temperature. Gas is expanded through one or more turbo-expanders, preferably reformed, and sent to a fuel cell where electricity, heat, carbon-dioxide, and water are generated. The carbon-dioxide is compressed by at least one compressor and piped downhole for sequestration. The turbo-expanders have shafts which preferably share the shafts of the compressors. Thus, energy given up by the natural gas in the turbo-expanders is used to run compressors which compress carbon dioxide for downhole sequestration. In one embodiment, the natural gas is applied to heat exchangers in order to generate a stream of liquid natural gas. The remainder of the gas is expanded through the turbo-expanders and processed in the reformer prior to being sent to the fuel cell. A shifter may be used between the reformer and fuel cell. A solid oxide fuel cell is preferred.

1. A natural gas power plant located at or near a methane-producing formation traversed by at least one borehole, the natural gas power plant comprising:
 a first piping coupled to said borehole, said first piping transporting said methane; 
 a turbo-expander coupled to said first piping, wherein said turbo-expander receives said methane produced from the borehole at a first pressure and generates work therefrom, said methane exiting said turbo-expander at a reduced pressure relative to said first pressure, said turbo-expander having a shaft; 
 a fuel cell and separator coupled to said turbo-expander, wherein outputs from said fuel cell and separator include electricity, heat, water, and carbon dioxide; 
 a compressor which receives said carbon dioxide and compresses it, wherein said compressor is mechanically coupled to said shaft of said turbo-expander; and 
 a second piping coupled to said compressor and transporting compressed carbon dioxide into a geological formation for sequestration therein. 
 
   
   
     2. A natural gas power plant according to  claim 1 , wherein:
 said compressor utilizes said shaft of said turbo-expander as a shaft of said compressor. 
 
   
   
     3. A natural gas power plant according to  claim 1 , further comprising:
 a reformer which couples said turbo-expander and said fuel cell and separator, said reformer receiving water and said methane from said turbo-expander and generating as outputs therefrom hydrogen gas and carbon monoxide. 
 
   
   
     4. A natural gas power plant according to  claim 3 , wherein:
 at least a portion of said water output from said fuel cell is used as said water provided to said reformer. 
 
   
   
     5. A natural gas power plant according to  claim 3 , wherein:
 said carbon monoxide and said hydrogen outputs from said reformer are provided to said fuel cell with oxygen, and said fuel cell generates said electricity, heat, and a carbon dioxide and water stream therefrom. 
 
   
   
     6. A natural gas power plant according to  claim 5 , wherein:
 said separator separates said carbon dioxide from said water in said stream. 
 
   
   
     7. A natural gas power plant according to  claim 6 , wherein:
 said fuel cell is a solid oxide fuel cell, and said oxygen is obtained from an air intake. 
 
   
   
     8. A natural gas power plant according to  claim 3 , further comprising:
 a shifter which receives said carbon monoxide and said hydrogen gas outputs from said reformer and utilizes said outputs together with water to generate a carbon dioxide and hydrogen gas stream, wherein said steam is provided to said separator which provides said hydrogen to said fuel cell which generates said electricity, said heat, and said water. 
 
   
   
     9. A natural gas power plant according to  claim 8 , wherein:
 said fuel cell is a solid oxide fuel cell with an air intake. 
 
   
   
     10. A natural gas power plant according to  claim 3 , further comprising:
 a heat exchanger which uses said heat from said fuel cell to heat at least one of said water and said methane utilized by said reformer. 
 
   
   
     11. A natural gas power plant according to  claim 10 , wherein:
 said heat exchanger heats both said water and said methane utilized by said reformer. 
 
   
   
     12. A natural gas power plant according to  claim 1 , wherein:
 said geological formation in which said carbon dioxide is sequestered is said methane producing formation. 
 
   
   
     13. A natural gas power plant according to  claim 12 , wherein:
 said borehole is a dual completion well from which said methane is obtained at a first depth and to which said carbon dioxide is sequestered at a second depth different from said first depth. 
 
   
   
     14. A natural gas power plant located at a methane-producing formation traversed by at least one borehole, the natural gas power plant comprising:
 a first piping coupled to said borehole, said first piping transporting said methane; 
 a reformer which receives water and said methane and generates as outputs therefrom hydrogen gas and carbon monoxide; 
 a solid oxide fuel cell and separator coupled to said reformer output, wherein outputs from said fuel cell and separator include electricity, heat, water, and carbon dioxide; 
 a compressor which receives said carbon dioxide and compresses it; and 
 a second piping coupled to said compressor and transporting compressed carbon dioxide into said formation for sequestration therein. 
 
   
   
     15. A natural gas power plant according to  claim 14 , further comprising:
 a turbo-expander coupled to said first piping, wherein said turbo-expander receives said methane produced from the borehole at a first pressure and generates work therefrom, said methane exiting said turbo-expander at a reduced pressure relative to said first pressure, said turbo-expander having a shaft, wherein said compressor is mechanically coupled to said shaft. 
 
   
   
     16. A natural gas power plant according to  claim 14 , wherein:
 said carbon monoxide and said hydrogen outputs from said reformer are provided to said solid oxide fuel cell with air, and said fuel cell generates said electricity, heat, and a carbon dioxide and water stream therefrom, and said separator separates said carbon dioxide from said water in said stream. 
 
   
   
     17. A natural gas power plant according to  claim 14 , further comprising:
 a shifter which receives said carbon monoxide and said hydrogen gas outputs from said reformer and utilizes said outputs together with water to generate a carbon dioxide and hydrogen gas stream, wherein said steam is provided to said separator which provides said hydrogen to said fuel cell which generates said electricity, said heat, and said water.